The invention relates to an axial piston machine having a device for the electrically proportional adjustment of the volumetric displacement according to the features of Claim 1.
Axial piston machines such as hydraulic pumps and motors in an open or closed circuit and of swashplate design or oblique-axis design are often actuated using an electrically proportional adjustment. The input signal into this adjustment unit is an electric current. Its output signal is a hydraulic pressure. The outgoing oil pressure acts on servopistons of the axial piston machine which thus move along their movement axis. This movement is transmitted, for example, to a swashplate which, by changing its angular position, changes the volumetric displacement of the axial piston machine.
The current position of the swashplate or oblique axis is fed back to the electrically actuated adjustment unit via a mechanical feedback system. By means of this feeding-back of the position, the control circuit is closed and it is ensured that the volumetric displacement of the axial piston machine also behaves proportionally to the electric current at the adjustment unit. The system has a control piston which moves by means of at least one proportional magnet, but generally is displaced along its movement axis by two proportional magnets which are arranged opposite one another at its end faces, and as a result connects or disconnects ducts in such a way that oil is made available at a specific pressure for moving the servopistons. In known axial piston machines, a lever and spring system is provided for this purpose, which system ensures that the angle of the swashplate or of the valve segment in relation to the oblique axis is fed back to the control piston.
Known feedback mechanisms have structurally induced problems. On the one hand, any form of mechanical hysteresis between levers, springs and proportional magnets adversely affects the desired proportional adjustment characteristic owing to the sensitive equilibrium of forces, and on the other hand previous solutions require differently dimensioned adjustment devices depending on the overall size of the axial piston machine, which adjustment devices give rise to large overall widths in some cases owing to the lever mechanisms which are used. The proportional magnets are then a correspondingly large distance apart from one another. Since they are mounted at an exposed location on the axial piston machine, this increases their risk of damage and makes it inappropriate to use such adjustment units on axial piston machines with a small volumetric displacement and correspondingly small installation space.
The invention is based on the object of providing an axial piston machine having an improved adjustment system.